I worry that you might approach a pharmacist or doctor with questions about rag control, and I'm sorry, I just don't see that going well.
The "medicine" you're looking for is just plain old birth control pills. While they certainly can cause people to be unable to become pregnant, that should not be a problem later (I hope much, much later) when your girlfriend is ready to have a baby. Regular pills will work if taken all month long, as will the fancy new ones sold specifically to limit a woman's period to four times a year (sold as Seasonale). Any of these will require a doctor's prescription, and I couldn't be happier about that. You guys sound a little unclear on a number of concepts, which is fine as long as you're not messing around with anything that could seriously screw up parts of her body if mishandled, like, oh, her endocrine system.